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San Bruno, California (CNN) -- Firefighters have fully contained a massive gas-fueled blaze in California that killed four people, while search efforts and attempts to determine the cause of the fire were still under way on Friday.

The fire triggered by a ruptured natural gas transmission line sent giant fireballs shooting 80 feet into the air in a quiet neighborhood of San Bruno, near the San Francisco airport.

"It looks like a moonscape in some areas," said San Bruno Fire Chief Dennis Haag, who was visibly shaken at a news conference.

Scorched homes and the shells of burned-out cars lined charred streets as firefighters battled hot spots and residents clamored to know the cause of their town's devastation. By Friday afternoon, the fire was reported to be fully contained.

California Lt. Gov. Abel Maldonado said he was shocked by the "horrible tragedy."

Gallery: Fire rips through California neighborhood

Video: Witnesses report smell of gas

Video: Photographer describes fire scene

Video: Firefighters battle San Bruno blaze

Video: Gas explosion levels neighborhood

"It looks like a bomb went off," he said. "I saw debris everywhere. It was a huge explosion."

"Our hearts go out to those impacted by this horrible disaster," said Maldonado. "Without warning many of these peoples' lives have been changed forever and my deepest prayers go out to everyone."

He said "we will find out soon" what caused the fire that erupted after 6 p.m. Thursday after a gas transmission line broke and triggered an explosion. Maldonado also told reporters on Friday he had received a telephone call from President Barack Obama, who offered his support.

Four people are known to have died in the fire, the lieutenant governor said. Another 52 people were injured, including three patients who were taken to a hospital with third-degree burns and four firefighters who suffered from smoke inhalation.

Rescue workers initially feared the death toll would climb higher as they combed through the smoldering scene with cadaver dogs.

But by Friday evening, no one in the area was unaccounted for and local fire officials had not received reports of any missing people, according to Haag. He said about 100 people had evacuated to shelters.

Pacific Gas and Electric Company President Chris Johns said Friday that the ruptured gas transmission line had been secured and no more gas is flowing through it.

He said survey teams are walking house to house to "make sure it is safe" for residents to return, and he promised that the company will be transparent in working with federal investigators to learn the cause of the blast.

The National Transportation and Safety Board launched an investigation Friday.

"At this point, it's too early to speculate as to what may have happened," NTSB Vice Chairman Christopher Hart told reporters. He said a team of investigators was working on scene to determine probable cause. The group's findings will be put into a report that may not be ready for as many as 18 months, Hart said.

"The radiant heat from the actual gas and the fireball was making it so that they couldn't even attack the homes that were on fire," said news photographer Bryan Carmody, who arrived at the scene shortly after the blaze began.

Water pressure in the area was low because the fire compromised a water main, California state Sen. Leland Yee told CNN affiliate KRON, so firefighters had to truck in water.

James Ruane, the mayor of San Bruno, said he talked to survivors of the blaze to assure them that the city will help them. He said he could tell how much the incident affected them.

"It was the look on their faces. They were still in shock," he said. "They were walking around but almost in a daze. It must have been horrific when it happened."

Tim Gutierrez, who lives in a neighborhood near where the blast occurred, told CNN affiliate KRON that people living in the area have smelled natural gas for the past three weeks.